Q. What do you mean by image precision and object precision? Describe z- buffer algorithm for visible surface detection.

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What do you mean by image precision and object precision?

Ans. Visible- surface detection algorithms are broadly classified according to whether they deal with object definitions directly or with their projection images. These two approaches are called object- space methods of object precision and image- space methods or image precision respectively. An object space method compares objects and parts of objects to each other within the scene definition to determine which surface, as a whole, we should label as visible. In an image- space algorithm, visibility is decided point by point at each pixel position on the projection plane. Most visible- surface algorithm use image- space methods, although object- space methods can be used effectively to locate visible surface in some cases. Line- display algorithms, on the other hand, generally use object- space methods to identify visible lines in wireframe displays, but many image- space visible- surface algorithm can be adapted easily to visible- line detection.